A NOTE ON THE MOUTHPARTS OF THE ARADIDAE 



C. S. Spooner. 



The members of the heteropterons family Aradidae are 

 supposed to represent the extreme of dorso-ventral flattening. 

 Certainly they are about as thin as we can imagine possible. 

 We are apt to think that their anatomy, both internal and 

 external, has been modified primarily in this direction. It was 

 with considerable surprise, therefore, that the author, in the 

 course of some morphological studies, discovered a modification 

 of the mouthparts unparalleled, so far as known, in the other 

 Hemiptera and which necessitates considerable dorso-ventral 

 space. 



This modification occurs in the mandibular and maxillary 

 setae and is confined to the interior of the head. The head 

 capsule is somewhat modified to accommodate these changed 

 conditions. It will be noticed (Fig. 1) that the clypeus and labrum, 

 known to systematists as the tylus, is curved ventrad and then 

 caudad in the arc of a circle. The suture separating the 

 clypeus and labrum is obsolete, a difference in texture and 

 flexibility marking its probable position. The lateral edges 

 of these sclerites are incurved and extend a considerable distance 

 within the head. These structures form a semicircular sheath. 



The mandibular and maxillary setae are articulated in the 

 normal position and become firmly interlocked soon after their 

 origin. They are then coiled, within the head, four or five 

 times anti-clockwise, then they bend sharply and reverse their 

 direction, coiling an equal number of times clockwise. They 

 leave the head capsule at the usual place, just cephalad of the 

 labium and lie in the groove along its dorsal aspect. These 

 coils are closely appressed and the cephalic half of the coil is 

 enclosed by the sheath formed by the clypeus and labrum. 



The mechanics of this arrangement are simple. A pull on 

 the proximal ends of the setae would result in the uncoiling of the 

 spring in both directions, forcing the distal end further out of the 

 head capsule. Thus the distance which these setae may be 

 protruded is Hmited only by the length and contractability of 

 the muscles concerned. 



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